If student A is attempting waza X which is supposed to result in a particular throw or a pin when attacked in manner Y and the result is neither a throw nor a pin then waza X is executed in an ineffective manner.

At this point it is student A's job to deconstruct and analyze his waza and address the lacking areas. Student A can then repeat the practice of Waza X with varying levels of resistance and counter attacks thrown in to increase the level difficulty and by extension, the level of skill required to achieve expected result.